It might be because he is not using nintendo's sdk anymore, particularly the "microcode" for RSP "coprocessor". Most N64 emulators usually do not emulate RSP properly, but detect which specific nintendo's microcode is used and then emulate it's behavior.

That means they are not accurate cores since it works fine on real hardware.

At the end of the video he says it needs real hardware or a "highly accurate emulator like Ares".